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Date:   Wed, 4 Jul 2018 00:20:49 -0700
From:   Andrei Vagin <avagin@...tuozzo.com>
To:     Amritha Nambiar <amritha.nambiar@...el.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        alexander.h.duyck@...el.com, willemdebruijn.kernel@...il.com,
        sridhar.samudrala@...el.com, alexander.duyck@...il.com,
        edumazet@...gle.com, hannes@...essinduktion.org,
        tom@...bertland.com, tom@...ntonium.net
Subject: Re: [net-next, v6, 6/7] net-sysfs: Add interface for Rx queue(s) map
 per Tx queue

Hello Amritha,

I see a following warning on 4.18.0-rc3-next-20180703.
It looks like a problem is in this series.

[    1.084722] ============================================
[    1.084797] WARNING: possible recursive locking detected
[    1.084872] 4.18.0-rc3-next-20180703+ #1 Not tainted
[    1.084949] --------------------------------------------
[    1.085024] swapper/0/1 is trying to acquire lock:
[    1.085100] 00000000cf973d46 (cpu_hotplug_lock.rw_sem){++++}, at: static_key_slow_inc+0xe/0x20
[    1.085189] 
[    1.085189] but task is already holding lock:
[    1.085271] 00000000cf973d46 (cpu_hotplug_lock.rw_sem){++++}, at: init_vqs+0x513/0x5a0
[    1.085357] 
[    1.085357] other info that might help us debug this:
[    1.085450]  Possible unsafe locking scenario:
[    1.085450] 
[    1.085531]        CPU0
[    1.085605]        ----
[    1.085679]   lock(cpu_hotplug_lock.rw_sem);
[    1.085753]   lock(cpu_hotplug_lock.rw_sem);
[    1.085828] 
[    1.085828]  *** DEADLOCK ***
[    1.085828] 
[    1.085916]  May be due to missing lock nesting notation
[    1.085916] 
[    1.085998] 3 locks held by swapper/0/1:
[    1.086074]  #0: 00000000244bc7da (&dev->mutex){....}, at: __driver_attach+0x5a/0x110
[    1.086164]  #1: 00000000cf973d46 (cpu_hotplug_lock.rw_sem){++++}, at: init_vqs+0x513/0x5a0
[    1.086248]  #2: 000000005cd8463f (xps_map_mutex){+.+.}, at: __netif_set_xps_queue+0x8d/0xc60
[    1.086336] 
[    1.086336] stack backtrace:
[    1.086419] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.0-rc3-next-20180703+ #1
[    1.086504] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
[    1.086587] Call Trace:
[    1.086667]  dump_stack+0x85/0xcb
[    1.086744]  __lock_acquire+0x68a/0x1330
[    1.086821]  ? lock_acquire+0x9f/0x200
[    1.086900]  ? find_held_lock+0x2d/0x90
[    1.086976]  ? lock_acquire+0x9f/0x200
[    1.087051]  lock_acquire+0x9f/0x200
[    1.087126]  ? static_key_slow_inc+0xe/0x20
[    1.087205]  cpus_read_lock+0x3e/0x80
[    1.087280]  ? static_key_slow_inc+0xe/0x20
[    1.087355]  static_key_slow_inc+0xe/0x20
[    1.087435]  __netif_set_xps_queue+0x216/0xc60
[    1.087512]  virtnet_set_affinity+0xf0/0x130
[    1.087589]  init_vqs+0x51b/0x5a0
[    1.087665]  virtnet_probe+0x39f/0x870
[    1.087742]  virtio_dev_probe+0x170/0x220
[    1.087819]  driver_probe_device+0x30b/0x480
[    1.087897]  ? set_debug_rodata+0x11/0x11
[    1.087972]  __driver_attach+0xe0/0x110
[    1.088064]  ? driver_probe_device+0x480/0x480
[    1.088141]  bus_for_each_dev+0x79/0xc0
[    1.088221]  bus_add_driver+0x164/0x260
[    1.088302]  ? veth_init+0x11/0x11
[    1.088379]  driver_register+0x5b/0xe0
[    1.088402]  ? veth_init+0x11/0x11
[    1.088402]  virtio_net_driver_init+0x6d/0x90
[    1.088402]  do_one_initcall+0x5d/0x34c
[    1.088402]  ? set_debug_rodata+0x11/0x11
[    1.088402]  ? rcu_read_lock_sched_held+0x6b/0x80
[    1.088402]  kernel_init_freeable+0x1ea/0x27b
[    1.088402]  ? rest_init+0xd0/0xd0
[    1.088402]  kernel_init+0xa/0x110
[    1.088402]  ret_from_fork+0x3a/0x50
[    1.094190] i8042: PNP: PS/2 Controller [PNP0303:KBD,PNP0f13:MOU] at 0x60,0x64 irq 1,12


https://travis-ci.org/avagin/linux/jobs/399867744

On Fri, Jun 29, 2018 at 09:27:07PM -0700, Amritha Nambiar wrote:
> Extend transmit queue sysfs attribute to configure Rx queue(s) map
> per Tx queue. By default no receive queues are configured for the
> Tx queue.
> 
> - /sys/class/net/eth0/queues/tx-*/xps_rxqs
> 
> Signed-off-by: Amritha Nambiar <amritha.nambiar@...el.com>
> ---
>  net/core/net-sysfs.c |   83 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 83 insertions(+)
> 
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index b39987c..f25ac5f 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -1283,6 +1283,88 @@ static ssize_t xps_cpus_store(struct netdev_queue *queue,
>  
>  static struct netdev_queue_attribute xps_cpus_attribute __ro_after_init
>  	= __ATTR_RW(xps_cpus);
> +
> +static ssize_t xps_rxqs_show(struct netdev_queue *queue, char *buf)
> +{
> +	struct net_device *dev = queue->dev;
> +	struct xps_dev_maps *dev_maps;
> +	unsigned long *mask, index;
> +	int j, len, num_tc = 1, tc = 0;
> +
> +	index = get_netdev_queue_index(queue);
> +
> +	if (dev->num_tc) {
> +		num_tc = dev->num_tc;
> +		tc = netdev_txq_to_tc(dev, index);
> +		if (tc < 0)
> +			return -EINVAL;
> +	}
> +	mask = kcalloc(BITS_TO_LONGS(dev->num_rx_queues), sizeof(long),
> +		       GFP_KERNEL);
> +	if (!mask)
> +		return -ENOMEM;
> +
> +	rcu_read_lock();
> +	dev_maps = rcu_dereference(dev->xps_rxqs_map);
> +	if (!dev_maps)
> +		goto out_no_maps;
> +
> +	for (j = -1; j = netif_attrmask_next(j, NULL, dev->num_rx_queues),
> +	     j < dev->num_rx_queues;) {
> +		int i, tci = j * num_tc + tc;
> +		struct xps_map *map;
> +
> +		map = rcu_dereference(dev_maps->attr_map[tci]);
> +		if (!map)
> +			continue;
> +
> +		for (i = map->len; i--;) {
> +			if (map->queues[i] == index) {
> +				set_bit(j, mask);
> +				break;
> +			}
> +		}
> +	}
> +out_no_maps:
> +	rcu_read_unlock();
> +
> +	len = bitmap_print_to_pagebuf(false, buf, mask, dev->num_rx_queues);
> +	kfree(mask);
> +
> +	return len < PAGE_SIZE ? len : -EINVAL;
> +}
> +
> +static ssize_t xps_rxqs_store(struct netdev_queue *queue, const char *buf,
> +			      size_t len)
> +{
> +	struct net_device *dev = queue->dev;
> +	struct net *net = dev_net(dev);
> +	unsigned long *mask, index;
> +	int err;
> +
> +	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> +		return -EPERM;
> +
> +	mask = kcalloc(BITS_TO_LONGS(dev->num_rx_queues), sizeof(long),
> +		       GFP_KERNEL);
> +	if (!mask)
> +		return -ENOMEM;
> +
> +	index = get_netdev_queue_index(queue);
> +
> +	err = bitmap_parse(buf, len, mask, dev->num_rx_queues);
> +	if (err) {
> +		kfree(mask);
> +		return err;
> +	}
> +
> +	err = __netif_set_xps_queue(dev, mask, index, true);
> +	kfree(mask);
> +	return err ? : len;
> +}
> +
> +static struct netdev_queue_attribute xps_rxqs_attribute __ro_after_init
> +	= __ATTR_RW(xps_rxqs);
>  #endif /* CONFIG_XPS */
>  
>  static struct attribute *netdev_queue_default_attrs[] __ro_after_init = {
> @@ -1290,6 +1372,7 @@ static struct attribute *netdev_queue_default_attrs[] __ro_after_init = {
>  	&queue_traffic_class.attr,
>  #ifdef CONFIG_XPS
>  	&xps_cpus_attribute.attr,
> +	&xps_rxqs_attribute.attr,
>  	&queue_tx_maxrate.attr,
>  #endif
>  	NULL

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